The invention relates generally to a photodetector, and more particularly to a photodetector including two or more avalanche-gain layered structures and multi-terminals.
Recently, research has been actively conducted for light reception (detection) devices that are used in ultra-high speed large-capacity optical communication systems, image processing systems, etc. The major objects of the developments were to enhance the speed and sensitivity of such devices. During recent years, along with the advancement of the semiconductor fabricating technologies such as molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), etc., semiconductor photoelectric devices having heterostructures have been developed.
Research into a bulk layer and a thin film thinner than 1000 xc3x85 of the materials such as GaSb/InAs, InAs/ZnTe, GaAs/Al(Ga)As, InGaAs/InAlAs/InP, etc. has been actively conducted using the energy bandgap engineering of the semiconductor heterostructure.
Also, research has been conducted regarding the phenomenon whereby light in the infrared-ray region is absorbed or emitted by the interband transition of electrons or the electron intersubband transition between quantum-confined states with a view to solving these technical problems.
In addition, studies on the absorption, generation and voltage-controlled tunability of infrared-ray, and high-speed performance of photodetecting devices have been actively undertaken. The applications of these technologies in the field of ultra-high speed light receivers, ultra-high speed switching devices and logic devices have technical importance.
Of the photodetectors that have been developed to solve these technical problems, the avalanche photodetector is advantageous due to its high sensitivity as compared to conventional PIN photodetectors. The avalanche photodetector, however, has the problems of requiring a very high voltage to obtain avalanche-gain, as well as having low speed and stability.
Conventional technologies concerning the avalanche photodetector may be briefly summarized as follows.
First, U.S. Pat. No. 5,539,221 issued to M. Tsuji and titled xe2x80x9cStaircase Avalanche Photodiodexe2x80x9d describes an electronic apparatus using the infrared-ray absorption effect of the semiconductor hetero-junction structure. The ""221 patent describes the operational principle of the photodetector, and its applications and improved characteristics.
The ""221 patent discloses a step-type avalanche photodetector including a periodic multi-layer structure graded into InGa(x)Al(1xe2x88x92x)As(x greater than 0.1) from InAlAs in order to improve the dark current characteristic. In other words, in case of an avalanche photodiode having separated light absorption layers and a multiplication layer, it must have an electric field relaxation layer having a greater energy band gap than the light absorption layer and also have a triple structure in which a heavily doped layer is sandwiched between lightly doped layers. The patent discloses a triple-structure layer comprising a multiplication layer including a periodic multilayer graded into InGa(x)Al(1xe2x88x92x)As(x greater than 0.1) from nxe2x88x92-InAlAs on a n-type InP substrate, a pxe2x88x92-InGaAs light absorption layer and a n-, p+, pxe2x88x92 type InP relaxation layer located between the light absorption layer and the multiplication layer. Utilizing this structure, the technology of the ""221 patent improves the dark current characteristic.
Also, U.S. Pat. No. 5,457,327 issued to xe2x80x98K. Taguchixe2x80x99 and entitled xe2x80x9cAvalanche Photodiode with an improved multiplication layerxe2x80x9d describes the operational principle of an photodetector, its application and improved characteristics.
The ""327 patent teaches a photodetector structure including a light absorption layer, an electric field relaxation layer and a multiplication layer, wherein the multiplication layer has a structure periodically laminating two different layers in order to improve the operation speed. In the structure, the energy band gap of the first type layer gradually increases toward the direction in which accelerated electrons are moving and the energy band gap of the second type layer gradually reduces toward the direction in which accelerated electrons are moving. By means of the structure, the ""327 patent improves the operation speed of the device.
The present invention is directed to solving the above problems and an object of the present invention is to provide an improved photodetector including a light absorption layer for detecting an infrared-ray being comprised of a single bulk-type material layer, a thin film layer, a quantum dots or quantum wires; more than two avalanche-gain layered structures each including a thin multiplication layer; and multi-terminals. The device of the present invention can obtain a high gain by applying a relatively low voltage, increase the sensitivity, provide multiple new functionalities due to the increased number of terminals and increase the stability of the device.
In order to accomplish the above objects, according to one aspect of the present invention, an avalanche photodetector is provided that includes an emitter light absorption layer located between a collector layer and an emitter layer (top contact layer) sequentially formed on a substrate, a plurality of avalanche-gain layered structures including a multiplication layer, a charge layer which controls the built-in potential and the electric field of the multiplication layer, and a contact layer located between the emitter light absorption layer and the collector layer.
According to another aspect of the invention, an avalanche photodetector is provided including an emitter light absorption layer structure located between a collector layer and an emitter layer (top contact layer) sequentially formed on a substrate, comprising a first avalanche-gain layered structure including a first multiplication layer formed on the collector layer, a first charge layer formed on the first multiplication layer and a contact layer formed on the first charge layer; and a second avalanche-gain layered structure including a second multiplication layer formed on the first avalanche-gain layered structure and a second charge layer formed on the second multiplication layer, wherein the emitter light absorption layer is stacked on the second avalanche-gain layered structure.
Further, according to still another aspect of the invention, a resonant cavity avalanche photodetector is provided including an emitter light absorption layer between a collector layer and an emitter layer (top contact layer) sequentially formed on a substrate, an underlying mirror structure formed between the substrate and the collector, an upper mirror structure formed on the emitter layer (top contact layer), a plurality of avalanche-gain layered structures including a charge layer, a multiplication layer and a contact layer between the light absorption layer and the collector layer.